In magnetic storage devices such as hard disk drives (HDD), read and write heads are used to magnetically read and write information to and from the storage media. In a HDD, data is stored on one or more disks in a series of adjacent concentric circles. A HDD comprises a rotary actuator, a suspension mounted on an arm of the rotary actuator, and a slider bonded to the suspension to form a head gimbal assembly (HGA). In a traditional HDD, the slider carries a write head and read head, and radially floats over the surface of the disk under the control of a servo control system that selectively positions a head over a specific track of the disk. In this one read head (reader) configuration, the reader is aligned over the center of a track for data read back.
As HDD storage capacities have increased, the data track separation has decreased and the density has increased. However, as adjacent tracks are moved closer together, noise interference from adjacent tracks during data read back, Inter-Track Interference (ITI), becomes an increasing concern. If there is too much ITI, data may not be readable from a track. This places a limitation on the storage density of traditional one reader head per slider hard disk drive assemblies.
Two-Dimensional Magnetic Recording (TDMR) has recently been developed for pushing magnetic media storage densities for hard disk drives (HDD) well beyond 1 Tb/in2. In TDMR HDD assemblies, the slider comprises a plurality of reader heads: at least one data track reader, and one or more ITI noise cancelling readers. In this arrangement, the ITI signals that corrupt the data being recovered from a data track of interest can be cancelled by reading at least one of the adjacent (interfering) tracks and using the read signals to cancel the ITI on the data read from the data track of interest. Current manufacturing process limitations, where adjacent readers are separated by at least two track pitches (center to center) require that these plurality of readers be manufactured on at least two or more layers separated by a longitudinal distance. There are, however, process variations during manufacture of the readers on different layers. In particular, photolithography limitations induce a variable Overlay Error (OLE) during manufacture. Accordingly, systems and methods for correcting this OLE are desired.